Hydrocarbons may contaminate both soil and ground water as a result of accidental spillage frcm storage tanks or pipes; accidents with transport vehicles; or even by intentional acts such as dumping. Typically, some hydrocarbon biodegradation occurs in the first three feet below the earth's surface. However, that portion of the spill below three feet largely remains in the soil. If the hydrocarbons are not isolated or removed, the spill can spread beyond the original area.
Various procedures have been proposed to address soil and ground water contamination by spilled hydrocarbons. Some systems require physical containment or removal, while others treat the spilled hydrocarbon in place. When the hydrocarbons are treated in place they may be evaporated or biodegraded under specific conditions.
Underground evaporation of spilled hydrocarbons may be achieved by forced venting. See U.S. Pat. Nos. 4,593,760, issued June 10, 1986 to Visser et al; 4,183,407, issued Jan. 15, 1980 and 3,980,138, issued Sept. 14, 1976, both to Knopic. However, this process is limited by the vapor pressure of the spilled hydrocarbons and the amount that can be evaporated. Since there is a limit on the amount of hydrocarbon that can be evaporated by venting, there is no incentive to go above that flow rate that provides the maximum evaporation.
Biodegradation has also been disclosed for underground hydrocarbons. U.S. Pat. No. 4,401,569 issued Aug. 30, 1983 to Jhaveri et al discloses a method and apparatus for treating hydrocarbon contaminated ground and ground water. Patentees disclose adding nutrients and gases to water that is flowed through the contaminated soil. A process of this type can be disadvantageous because: the irrigation water washes some hydrocarbons or other contaminants (toxic metal salts, etc.) into the water table; water carries a limited amount of oxygen (8 ppm) into the soil which limits the amount and the rate of degradation that may take place; irrigation can limit biodegradation by physically channeling oxygen-carrying fluids away from the hydrocarbon contaminated (oily) dirt; and, water and oil are immiscible so that biodegradation is limited to water/oil surfaces.
Accordingly, there is the need for a process that will rapidly decontaminate hydrocarbon contaminated soil in an efficient and an environmentally acceptable manner. The need has now been satisfied by the invention that is described below.